Bronze glass has found particular utility for architectural applications as building glass and has been considered for automotive glass applications. Glass is generally defined by certain spectral properties like dominant wavelength, excitation purity, and light transmission. The lower the excitation purity of a color, the closer it is to being a so-called neutral color which does not distort the hues of objects seen through it.
Those skilled in the art know that dominant wavelength, purity and light transmission all vary unpredictably with one another. Consequently, developing a new glass composition having a particular color, purity and light transmission value may be difficult. For example, an experimental change in the amount or relative proportions of one or more colorants in a glass composition intended to bring one of these numerical values closer to a target value may cause one or both of the other values to drift off target.
Numerous patented bronze glasses which have been manufactured using as colorants iron oxide, cobalt oxide, chromium oxide and selenium or nickel oxide. Still other significantly different colored patented glasses have also been made from these same colorants, as would be appreciated, however, in different colorant proportions. And yet these different colored glasses can include one or more of these colorants in the same amount. For example, increasing the amount of cobalt in a brown or bronze glass made from iron oxide, cobalt oxide, and selenium, results in a blue glass. The difference is the spectral properties including color of the resultant glass is thus closely related to the specific proportions of the colorants in the glass. Hence, those skilled in the art appreciate the unpredictable and time consuming effort required to formulate new glass compositions.
Bronze glasses have been developed using the colorants defined above, where the selenium or nickel oxide imparts a bronze color. However, the inclusion of nickel oxide as a colorant is generally undesirable because it can lead to the formation of nickel sulfide stones during the melting process which can later affect the quality of the glass. Nickel free bronze glass have been proposed, e.g., in U.S. Pat. No. 3,296,004 ('004), U.S. Pat. No. 5,565,388 ('388), and U.S. Pat. No. 5,656,560 ('560). The '004 patent discloses a brown glass whose colorants consist essentially of: iron oxide, cobalt oxide and selenium, while the '388 patent discloses a high transmittance bronze glass whose colorants consist essentially of iron oxide, and selenium with optionally cobalt oxide, nickel oxide, or chromium oxide. Patent '560 also discloses a light bronze-tinted or grey-tinted glass, in this instance containing a high level (0.5-2.0 wt. %) of manganese oxide as colorant and optionally one or more of the following colorants: iron oxide, vanadium oxide, nickel oxide, copper oxide, and cobalt oxide. As discussed above, similar colorants, but in different proportions can lead to different glass colors as seen from U.S. Pat. No. 5,346,867 disclosing a neutral grey glass which contains iron oxide, cobalt, selenium and manganese oxide as colorants. Another nickel-free glass is disclosed in U.S. Pat. No. 4,104,076. It uses iron oxide and cobalt oxide with optional chromium oxide, uranium oxide, and selenium as colorants to make a bronze or gray colored glass.
Still other U.S. patents disclose bronze glass. For example, U.S. Pat. No. 4,101,705, discloses an automotive glass product with high transmittance and a neutral bronze color employing iron oxide and selenium as essential colorants and optionally any combination of cobalt, nickel, or chromium oxides colorants. U.S. Pat. No. 4,190,452 generates a bronze colored glass product using iron oxide and selenium with optional quantities of cobalt oxide, nickel oxide, and chromium oxide as colorants. Another bronze colored glass product is taught in U.S. Pat. No. 5,380,685 using the colorants of iron oxide, cerium oxide, cobalt oxide and selenium.
U.S. Pat. No. 3,481,750 discloses a special method of making a different type of brown colored glass that is termed an amber glass using high levels of colorants of iron oxide, manganese oxide, and cerium in a frit mixture that is intended to be added late in the process of glass making in the forehearth of a glass tank that makes bottles. Another different color of brown glass is disclosed in U.S. Pat. No. 3,844,796 where low concentrations of iron oxide with manganese and chromium oxides are used to make a chocolate brown colored glass for bottles, pressed ash trays, glasses and the like.
Generally, bronze architectural glasses are manufactured by coating a high transmittance, light bronze colored glass with a coating to darken it and to filter out visible, UV and IR radiation. As would be appreciated, reducing transmission of this radiation is particularly necessary if the glass is to be used in high sunshine geographic areas. As would be appreciated, applying such a coating adds another step to the glass manufacturing process and can introduce quality control issues for the coating in the final product.
We have invented a new dark bronze glass composition different from those described above which includes specifically defined amounts of iron oxide, manganese oxide, selenium, and optionally cobalt oxide as colorants. This new dark bronze glass has improved UV and IR absorbing properties and is particularly useful for architectural applications. In addition, the new glass has defined spectral properties including dominant wavelength (color). The pleasing relatively dark bronze color is able to be obtained without adding undesirable colorants like nickel oxide or chromium oxide to the glass, and without the necessity for an applied surface coating to enhance the dark bronze color and improve the UV and IR absorbing properties. And we have found that the bronze glass desirably can be manufactured without the use of nitrates often added when oxidizing conditions are desired in the furnace during glass melting. It is known that the use of nitrates can contribute to NOx emissions.
Advantageously, we have also found that the particular claimed formulation of the invention glass allows for increased amounts of iron oxide to be included in the glass without darkening the color, while at the same time increasing the UV and IR absorbing properties of the glass. As would be appreciated, the UV and IR light absorption properties of a glass are especially valuable when the glass is used for buildings. When heat is absorbed by the glass, the load on building air conditioners is reduced and when the ultra violet absorption is improved, there is less damage over time to the colors of articles inside the building, additionally providing for more occupant comfort. Therefore, controlling these spectral properties of the glass is very important. These spectral properties of the present invention dark bronze glass are particularly useful in sunny geographic areas, i.e., light is allowed to enter but more of the UV and IR radiation is filtered out by the glass. Hence, the present invention dark bronze glass overcomes the deficiencies of prior art glasses and is particularly useful as architectural glass and its method of manufacture provides additional benefits as will be explained in more detail below.